Heavy Duty Gas Turbine Research Articles

TGSim Plus™—Real-Time Dynamic Simulation Suite of Gas Turbine Systems for the MATLAB®/Simulink® Environment

Dynamic simulation of turbomachinery by Hardware in the Loop (HIL) real-time systems has become an essential practice, due to the high cost of real equipment testing and the need to verify the control and diagnostic systems’ reaction to emergency situations. The authors developed a full model of a power generation Gas Turbine Plant, including liquid and gaseous auxiliaries, and the electrical generator and starter motor, integrated in a MATLAB®/Simulink® simulation suite: TGSim Plus™. This allows assembling models of various gas turbine (GT) architectures by customised Simulink® library blocks and simulating steady state and transient conditions, such as complete start-up and shutdown operations as well as emergency, contingent operations and artificially injected fault scenarios. The model solver runs real-time steps at milliseconds scale. The paper describes the main modelling characteristics and typical results of steady state and transient simulations of a heavy-duty gas turbine under development by Doosan Heavy Industries and Construction (Changwon, South Korea). Comparison with benchmark design simulations obtained by a reference non real-time software shows a good match between the two environments, duly taking into account some differences in the GT models setting affecting parts of the sequence. The paper discusses also the bleed streams warm-up influence on GT performance and the start-up states trajectories dependency on control logic and on the starter helper motor torque envelope.

Optimization of Flow Matching Schemes for a Heavy Gas Turbine Burning Syngas

A heavy-duty gas turbine, designed for natural gas, was used to burn the syngas with two different calorific values. This study was mainly to optimize the flow matching scheme for the gas turbine. Two models of gas turbine burning syngas with different calorific values were established and the calculation models of different flow matching schemes were provided. The optimum scheme was obtained by evaluating thermal efficiency and work output under different operating conditions. The results showed that the highest unit efficiency was achieved by, without significant drop in work output, increasing the throat area of the turbine nozzle and reducing the initial temperature of the gas. On the premise of ensuring the safety of the gas turbine unit, increasing the pressure ratio of the compressor could further improve the unit efficiency and the work output. Simply adjusting the angle of the inlet guide vane fails to match the flow of compressor and turbine. The measures such as reducing inlet temperature of turbine or air bleed still need to be adopted, but the thermal efficiency dropped significantly in this process.

Effect of Steam Injection on the Performance of Heavy-Duty Gas Turbines (Dept. M (Power) )

Effect of Steam Injection on the Performance of Heavy-Duty Gas Turbines (Dept. M (Power) )

Impact of a Combustor–Turbine Interface on Turbine Vane Aerodynamics and Film Cooling

Abstract Optimizing the aerothermal performance of the combustor–turbine interface is an important factor in enhancing the efficiency of heavy-duty gas turbines. Also, it is a key requirement to fulfill the lifetime in this hottest area of the gas turbine. Typically transition pieces of can combustors induce a highly nonuniform swirling flow at the turbine inlet. In order to better understand the impact of the nonuniform combustor flow at the first stage vanes, a combined experimental and numerical study was carried out. The experimental facility consisted of a high-speed linear cascade with four vane passages, including an upstream transition piece, which was representative of a heavy-duty gas turbine can combustor–turbine interface geometry. The experiments were conducted at engine representative Mach numbers, and film cooling effectiveness measurements were performed at three different blowing ratios. Computational fluid dynamics (CFD) Reynolds-averaged Navier–Stokes simulations were undertaken using a commercial flow solver. The numerical model was first validated with the experimental data, using inlet traverse five-hole probe measurements, pressure taps along the airfoil perimeter, and oil flow visualization results. The investigation shows that the position of the vane relative to the combustor transition piece has a significant impact on the vane aerodynamics and also film cooling behavior. This understanding was important for a robust first vane aerothermal design of the GT36.

Gas turbine efficiency and ramp rate improvement through compressed air injection

With the transition to more use of renewable forms of energy in Europe, grid instability that is linked to the intermittency in power generation is a concern, and thus, the fast response of on-demand power systems like gas turbines has become more important. This study focuses on the injection of compressed air to facilitate the improvement in the ramp-up rate of a heavy-duty gas turbine. The steady-state analysis of compressed airflow injection at part-load and full load indicates power augmentation of up to 25%, without infringing on the surge margin. The surge margin is also seen to be more limiting at part-load with maximum closing of the variable inlet guide vane than at high load with a maximum opening. Nevertheless, the percentage increase in the thermal efficiency of the former is slightly greater for the same amount of airflow injection. Part-load operations above 75% of power show higher thermal efficiencies with airflow injection when compared with other load variation approaches. The quasi-dynamic simulations performed using constant mass flow method show that the heavy-duty gas turbine ramp-up rate can be improved by 10% on average, for every 2% of compressor outlet airflow injected during ramp-up irrespective of the starting load. It also shows that the limitation of the ramp-up rate improvement is dominated by the rear stages and at lower variable inlet guide vane openings. The turbine entry temperature is found to be another restrictive factor at a high injection rate of up to 10%. However, the 2% injection rate is shown to be the safest, also offering considerable performance enhancements. It was also found that the ramp-up rate with air injection from the minimum environmental load to full load amounted to lower total fuel consumption than the design case.

Stress variation of a gas turbine tie-bolt rotor with Hirth serrations considering assembling and thermal effects

Tie-bolt rotors are commonly applied in heavy-duty gas turbines due to a better stiffness-mass ratio behavior compared to traditional integral rotors. In order to achieve a steady transformation from mechanical energy to electricity, the clamping force of the bolt is critical to keep multiple disks as a whole unit. However, the tensile stress of the bolt is changing during rotor assembly as well as operational conditions that should be considered carefully for the rotor safety. Moreover, subjected to mechanical as well as thermal loads, the stress of the rotor disks is a complicated mixture by different applied forces. In this manuscript, the preload variation during the process of rotor assembling is studied analytically with the help of the stiffness analysis. Then, a steady thermal analysis is performed with appropriate boundary conditions. Making use of the thermal-mechanical approach, a steady-stress distribution under different load combinations is achieved. Furthermore, a thorough insight into the stress level as well as the contact pressure of Hirth serrations is presented.

Failure of Impingement Cooling Plates in Gas Turbine Vanes

Abstract Impingement cooling plates welded to the inner shrouds of first-stage turbine vanes were found cracked after refurbishment, before installation in a heavy-duty gas turbine engine. The metallurgical root cause of the failure was determined to be embrittlement and surface melting from thermal over-exposure. This was not brought about by engine service, but was a result of the complex repair process, part of which are several heat treatment operations. The latter are tailor-made for the base alloy of the turbine vanes. For the lower-grade impingement cooling plates, however, the peak temperature from these furnace runs was too high. They should have been removed from the vanes prior to the high-temperature heat treatment operations, but were left attached to the vanes for cost reasons.

Thermal failure of a second rotor stage in heavy duty gas turbine

The impulse mode of operation and the supply of various types of fuels causes frequent failures even in the heavy duty gas turbines. The paper presents the ravages of second rotor stage failure in a gas turbine. The excessive thermal elongation rise caused by fuel change was indicated as the main cause. We applied nonlinear numerical analysis, preceded by thermodynamic calculations of the turbine and visual inspection of the effects of failure. Simulations were performed on undamaged blade geometry under load resulting from combustion: nominal fuel and the changed fuel. Thermodynamic calculations demonstrated a 70 °C increase in temperature using the changed fuel. The blade tip displacements demonstrated the possibility of abrasion. The amount of displacement of the tip of the turbine blade with increasing pressure or increasing rotational speed do not pose as great a threat, as does the increase in the temperature. To maintain long-term and safe operation of a gas turbine, it is necessary to strictly observe the manufacturer's guidelines regarding fuel composition. If during the operation of a gas turbine it is likely that it can be powered by various types of fuels, then the structure should have adequate effort reserves and working tolerances.

Study on combustion and emission characteristics of a heavy-duty gas turbine combustor fueled with natural gas

In this paper, the ignition delay and laminar combustion characteristics of natural gas were tested in a chemical shock tube and a constant volume combustion reactor, respectively, and simulated with the Gri_3.0, USC_2.0 and NUI_Galway models, respectively. It is proved that the ignition delay and laminar combustion characteristics of natural gas simulated with the Gri_3.0 model are in better agreement with the experiment than the USC_2.0 and NUI_Galway models. Furthermore, the simulated variation trends of the mole fractions of main species, especially NO and NO2 with temperature by the Gri_3.0 model are in better agreement with the experimental data in the oxidation of natural gas. The combustion process and pollutants generation characteristics in a single flame tube of a heavy-duty gas turbine burning natural gas were simulated by coupling the Gri_3.0 model with the computational fluid dynamics. It is shown that the simulated average temperature and the NOx concentration at the outlet of the flame tube are slightly higher than the experimental value by 8.06% and 5.08%, respectively. Because the NOx emission is higher than the designed value, fuel flows in the annular, main, and pilot combustion zones of the flame tube were reassigned and effects of the fuel redistributions on the NOx emission characteristics were investigated. It is shown that the NOx concentration at the outlet of the flame tube increases from 157.1 mg/m3 to 175.5 mg/m3 when the fuel flow in the pilot combustion zone is redistributed to the main combustion zone, and decreases from 157.1 mg/m3 to 139.51 mg/m3 when the fuel flow in the pilot combustion zone is redistributed to the annular combustion zone. The research results will provide theoretical basis and technical support for the optimization of this gas turbine operation.

Failure of a Swivel Arm in a Turning Gear Assembly

Abstract Swivel arms in a turning gear application failed in service due to fatigue cracking. 2 out of 52 components were affected. Turning gears are mainly used to spin heavy-duty gas turbine engines rotors after shut-down to prevent distortion of the still-hot rotor. The design of the swivel arms, that was not robust enough to tolerate deviations in fabrication, was identified as the root cause of the failures.

Generation characteristics of thermal NOx in a double-swirler annular combustor under various inlet conditions

The NOx emission of gas turbine is a key factor of air pollution. It is still a challenge to realize low-NOx generation for all the gas turbines with diverse types of combustors and operation schemes. In this study, a three-dimensional simulation of the internal flow and combustion in a double-swirler annular combustor of a heavy-duty gas turbine was carried out. The realizable k-ε turbulent model and finite rate/eddy dissipation combustion model were employed for the numerical calculation. The effects of the swirl number and temperature of the inlet premixed gas flow on the thermal performance and the relationship between the velocity-temperature field synergy and the thermal NOx formation were investigated on the basis of field synergy principle. The results indicated that the change of the outer swirl number had a greater impact on thermal NOx generation than the change of the inner swirl number. The velocity-temperature field synergy in the combustor became better as the inlet swirl number or the inlet gas temperature increased. This synergy had a correlation with the thermal NOx generation. The formation rate of thermal NOx in the combustor should be controlled with the optimized velocity-temperature field synergy rather than the sole reduction of inlet gas temperature by considering the required thermal uniformity and capacity. The adopted field synergy is a promising concept to evaluate the thermal related performance of combustor. The obtained results on the generation characteristics under various inlet conditions may guide the design and operation of gas turbine combustors.

Metallurgical Investigation of Cold-formed Fillet Pieces Made of Metastable Austenitic Stainless Steel, for the Turbine Exhaust Casing of a Heavy-Duty Gas Turbine Engine

Abstract With a novel class of heavy-duty gas turbine engines, turbine exhaust temperatures are expected to further increase. There are concerns that the propensity to cracking in service of the welded turbine exhaust casing (TEC) liners might also increase. Cold-formed “collars”, featuring large stress-reducing fillet radii, were designed to decrease thermal stresses in the welds, where the struts of the turbine bearing casing are aerodynamically clad by liner plates. Such collars were received from a supplier in the course of a product and process qualification (PPQ). The results of the metallurgical investigation ordered by an internal client are the subject of this contribution. It was found that deformation martensite was present in the subject cold-formed fillet pieces, despite a pre-heat of 150 °C and a post-fabrication 920 °C annealing process. However, the amount of deformation martensite found, at below 5 % volume fraction, was considered not to be detrimental for engine operation.

An efficient electromagnetic and thermal modelling of eddy current pulsed thermography for quantitative evaluation of blade fatigue cracks in heavy-duty gas turbines

The blade surface fatigue cracks often occur during service of Heavy-Duty Gas Turbines (HDGT) in high temperature, high rotational velocity and high frequency vibration environment. These fatigue cracks seriously threaten the safe operation of heavy-duty gas turbines, which would cause significant hazard or economic loss. The quantitative evaluation of blade surface fatigue cracks is extremely significant to HDGT. Eddy current pulsed thermography (ECPT) is an emerging non-destructive testing technology and show great potential for fatigue crack evaluation. This paper proposes a novel electromagnetic and thermal modelling of ECPT to achieve fast and effective quantitative evaluation for surface fatigue cracks. First, the proposed numerical method calculates electromagnetic field using the reduced magnetic vector potential method in the frequency domain based on frequency series method. The thermal source is transformed to an equivalent and simple form according to the energy equivalent method. Second, the temperature signals of ECPT are calculated through the time-domain iteration strategy with a relatively large time step. Then the ECPT experimental setup is established and the developed simulator is validated numerically and experimentally. The developed simulator is five times faster than the previous one and can be applied to eddy current thermography (ECT) with any kind of excitation waveforms. Finally, the depth of surface fatigue crack is quantitatively evaluated by means of the developed simulator, which is not only a promising simulation progress for ECPT, but also can be an effective tool embedded HDGT though-life maintenance.

Porosity-Driven Approaches to Model Fouling Effects on Flow Field

AbstractAir contamination by solid particles represents a real hazard for compressors for both heavy-duty and aeropropulsion gas turbines. Particles impacting the inner surfaces of the machine can stick to such surfaces or erode them. The presence of deposits entails a reduction in performance, in a phenomenon commonly referred to as fouling. As the severity of the problem increases, the performance reduction can become so big to demand engine shut down and offline washing. Numerical modeling is one of the techniques employed for tackling the fouling problem. In this work, an innovative procedure is proposed to evaluate the losses and the variation in the fluid flow due to the deposits. Specifically, as the deposit grows, it is assumed that it forms a porous medium attached to the wall. The porosity of this zone (related to the packing of the particles and to the number of particles that sticks to that portion of the wall) is responsible for the deposition-induced losses. Different approaches to compute such losses are proposed and discussed. By using this methodology, the two main effects of fouling (variation in roughness and in shape of the airfoil) can be easily included in a comprehensive analysis of the variation of the performance of the compressor over time. Furthermore, this approach overcomes the difficulties that may arise by using a mesh morphing technique. The computational grid is not modified, and thus, its quality is retained, without remeshing requirements, even for large deposits.

Numerical Investigations of Pollutant Emissions From Novel Heavy-Duty Gas Turbine Burners Operated With Natural Gas

Abstract A numerical investigation of pollutant emissions of a novel dry low-emissions burner for heavy-duty gas turbine applications is presented. The objective of this work is to develop and assess a robust and cost-efficient numerical setup for the prediction of NOx and CO emissions in industrial gas turbines and to investigate the pollutant formation mechanisms, thus supporting the design process of a novel low-emission burner. To this end, a comparison against experimental data, from a recent experimental campaign performed by BHGE in cooperation with University of Florence, has been exploited. In the first part of this work, a Reynolds-averaged Navier–Stokes (RANS) approach on both a simplified geometry and the complete domain is adopted to characterize the global flame behavior and validate the numerical setup. Then, unsteady simulations exploiting the scale adaptive simulation (SAS) approach have been performed to assess the prediction improvements that can be obtained with the unsteady modeling of the flame. For all simulations, the flamelet generated manifold (FGM) model has been used, allowing the reliable and cost-efficient application of detailed chemistry mechanisms in computational fluid dynamics (CFD) simulation. However, FGM typically faces issues predicting flame emissions, such as NOx and CO, due to the wide range of time scales involved, from turbulent mixing to pollutant species oxidation. Specific models are typically used to predict NOx emissions, starting from the converged flow-field and introducing additional transport equations. Also CO prediction, especially at part-load operating conditions could be an issue for flamelet-based model: in fact, as the load decreases and the extinction limit approaches, a superequilibrium CO concentration, which cannot be accurately predicted by FGM, appears in the exhaust gases. To overcome this issue, a specific CO-burn-out model, following the original idea proposed by Klarmann, has been implemented in ANSYS fluent. The model allows to decouple the effective CO oxidation term from the one computed by FGM, defining a postflame zone where the source term of CO is treated following the Arrhenius formulation. In order to support the design process, an indepth CFD investigation has been carried out, evaluating the impact of an alternative burner geometrical configuration on stability and emissions and providing detailed information about the main regions and mechanisms of pollutants production. The outcomes support the analysis of experimental results, allowing an indepth investigation of the complex flow-field and the flame-related quantities, which have not been measured during the tests.

Blade synchronous vibration measurements of a new upgraded heavy duty gas turbine MGT-70(3) by using tip-timing method

The work described in this paper is part of a comprehensive prototype test conducted on a heavy duty power generation gas turbine recently upgraded by MAPNA Turbine Engineering and Manufacturing Company (TUGA). A Blade tip-Timing system is proposed to determine the synchronous vibration characteristics of the rotor blades and to validate the design calculations. The last three stages of turbine section are equipped with tip-timing sensors. Six probes are positioned along the circumferential direction for each stage. The locations of sensors are accurately chosen based on the values of the natural frequencies and the number of necessary modes needed to be captured. The vibration parameters of the blades are obtained by post-processing and analyzing of the acquired data. The resonance frequencies are plotted against rotating speed during transient acceleration of the machine and the damping and amplitude of vibration in resonance condition are also determined. The obtained results meet the designer expectations and confirm a safe operation from vibrational point of view.

A Dynamic Firefly Algorithm-Based Fractional Order Fuzzy-PID Approach for the Control of a Heavy-Duty Gas Turbine

Heavy duty gas turbines have long played an important role in energy production. Advanced turbine designs are expected to be highly efficient, able to quickly ramp the output power up and down and promptly tolerate loading variations without breaching emissions regulations. Control design plays an important role in ensuring high efficiency and performance of gas turbines. This paper proposes a fractional order fuzzy-PID approach for a heavy-duty gas turbine. The controller gains are optimized using a Firefly algorithm enhanced with a dynamic parameter selection. This latter is used to speed up the convergence rate of the Firefly algorithm, optimize the gains of the fractional order fuzzy-PID and enhance the performance and efficiency of the gas turbine. The proposed approach is implemented to the speed loop of a gas turbine in order to maintain the output temperature and the turbine’s speed within their desired values during either a sudden change in loading or a drop in frequency. A comparison analysis with a standard Firefly algorithm-based approach was carried out to further assess the performance of the proposed evolved firefly algorithm-based approach.

Solidification Cracking in Manually TIG-Brazed T/C Installations of Novel AM Gas Turbine Burner Component

Abstract Serial fabrication of novel selective laser melted (SLM) heavy-duty gas turbine burner parts was established. This is an additive manufacturing (AM) process. Thermocouples (T/C) are manually tungsten inert gas (TIG) brazed to these components. After fabrication, they exhibited severe cracking within the brazed T/C joints and had to be scrapped. A laboratory order for a destructive metallographic investigation was placed by the client with the aim of determining the metallurgical cause of the cracking. The crack path is interdendritic. The crack propagated within the braze metal only. The crack morphology is consistent with solidification cracking (SC), a hot cracking mechanism. No evidence of liquid metal embrittlement, or LME, was found.

Failure analysis of first stage nozzle in a heavy-duty gas turbine

First stage nozzles are considered as one of the most critical components in the heavy-duty gas turbines because of their operational in-service condition in the hot gas path. In the present research, the failure analysis of a first stage nozzle in a159 MWgas turbine is investigated in order to specify the modes and mechanisms of the failure and their root causes. Various examinations including macroscopic and visual inspection of the nozzle outer surface, the micro examination of the fracture surface, chemical analysis and metallographic analysis were carried out to complete the investigation. The micro and macro examinations revealed cracks, erosion and oxidation damages in the nozzle investigated. These failures were caused by overheating and improper filtration of the turbine inputs which activated the thermal fatigue failure mode. Finally, in order to estimate the nozzle life and predict the failure occurrence, a modified model is developed using Robinsons rule and its extension for total damages of first stage nozzle based on statistical data gathered in a periodic inspection conducted during operation.

Effect of Natural Gas Composition on Low Nox Burners Operation in Heavy Duty Gas Turbine

Abstract Development of lean-premixed combustion technology with low emissions and stable operation in an increasingly wide range of operating conditions requires a deep understanding of the mechanisms that affect the combustion performance or even the operability of the entire gas turbine. Due to the relative wide range of natural gas composition supplies and the increased demand from Oil&Gas customers to burn unprocessed gas as well as liquified natural gas (LNG) with notable higher hydrocarbons (C2+) content, the impact on gas turbine operability and combustion related aspects has been matter of several studies. In this paper, results of experimental test campaign of an annular combustor for heavy-duty gas turbine are presented with focus on the effect of fuel composition on both emissions and flame stability. Test campaign involved two different facilities, a full annular combustor rig and a full-scale prototype engine fed with different fuel mixtures of natural gas with small to moderate C2H6 content. Emission trends and blowout for several operating conditions and burner configurations have been analyzed. Modifications to the burner geometry and fuel injection optimization have shown to be able to reach a good tradeoff while keeping low NOx emissions in stable operating conditions for varying fuel composition.